You must remember, as strait laced as Hagen was, he was in the mafia. It was just oh so common to have a mistress when in the mafia, especially at the time. Sonny did it, of course, Fredo did it, my guess is that Micheal did it from his confession, Carlo did it, and Tom did it.

But what I liked is how FFC showed this all in different ways among the guys. The showed Sonny as a hornball, Carlo as a scumbag, Fredo as the guy you can always have fun with, Tom as the quiet hornball, and Micheal as sort of evil all through how they cheated on their wives.

Thats Coppala/Puzo magic right there that we see oh so often.